Reaction bonding of open cell SiC-Al2O3 composites

Based on the reaction-bonding aluminum oxide (RBAO) technology, open cell SiC-Al2O3 composites with high strength were fabricated from aqueous slurry by a replication process with polyurethane sponges as the substrates. TGA reveals that about 18 wt% of the initial Al powder in the start compositions oxidized after 1 h stirring. Mixing procedure has a strong effect on the slurry rheological behavior and macrostructure of ceramic foams. The slurry prepared by stirring 1 h has a high viscosity and thixotropic behavior, which makes it uniformly coat the sponge substrate, resulting in the production of a ceramic with a uniform macrostructure. But, due to the emission of a lot of gas arising from the dramatic oxidation of the Al powder during milling, a large number of air bubbles are introduced in the slurry, and this is detrimental to the macrostructure of the ceramic foam. The phase compositions of the samples consist of silicon carbide, alumina, cristobalite, and mullite after sintering at 1350°C with a 1-h hold. Compressive strength increases as the Al powder content increases, and reaches 2.89 MPa with a 12 wt% Al powder for ceramic foams with a relative density of 0.30.